The present invention relates to smoke detection apparatus, and more particularly, to apparatus for detecting the presence of smoke or other solids in response to changes in light effects within a housing chamber.
It has become widely recognized that early and reliable indication of the presence of smoke in a building or the like can be very effective in saving lives inasmuch as many victims are killed due to smoke inhalation rather than to fire.
A variety of apparatus has been proposed heretofore for the purpose of early detection of the presence of smoke. It has become a common practice to provide apparatus including an exciter lamp or light source which functions to illuminate a dark space in which particulate matter such as smoke is to be detected. One such form of apparatus includes a pair of photocells which are judiciously arranged so that variations with age, temperature, applied voltage, etc. will be compensated for due to the connection of the pair of virtually identical cells in a balanced circuit arrangement.
In order to provide a representative sample of prior art schemes for smoke detection so as to furnish background for the subject matter of the present invention, reference may be made to the following U.S. Pat. Nos. 3,409,885, 3,723,747 and 3,727,056. Reference may also be made to copending application Ser. No. 489,076, now U.S. Pat. No. 3,980,997 to the assignee of the present invention.
A fundamental object of the present invention is to provide a number of improvements for a smoke detector of the type described in the aforesaid copending application, namely, a smoke detector which can exploit the inherent advantages of a solid state, low illumination level lamp as the light source. One particular light source that has been found to be especially efficacious is a light emitting diode, which has an extremely long life of over twenty years.
A more particular object is to improve upon the simulating device or technique which serves to test the correct functioning of the smoke detection apparatus.
A further object is, through the use of the aforesaid solid state light source, to provide a small, portable, inexpensive and reliable unit that can be employed in the home and which will not require frequent servicing.
Another specific object is to enable a simplified adjustment of the ratio of resistances utilized in a bridge network in respect to the particular resistance values encountered for the photocells of the smoke detector.
Another specific object is to provide a precisely configured sensor head, said sensor head containing both the low level light emitting source and the reflected cell of the pair of photocells used in the system.
Yet another object of the invention is to provide a smoke detector in which it is insured that a significant flow of air will constantly be maintained through the detector so that the smoke content can be continuously monitored.
The improved features of the present invention are in the context or environment of an apparatus for detecting the presence of smoke, which apparatus comprises a housing defining an enclosure for the detector; a detection chamber within the enclosure for permitting the continuous air flow; a low level light source mounted within the enclosure; and first and second light receiving means in the form of photocells mounted within the enclosure; a sensing circuit, including a threshold means, the sensing circuit being connected to the pair of photocells and responding to a change in the illumination due to the presence of smoke so as to activate an alarm signal means and thereby provide a warning of the presence of smoke.
The specific object of an improved simulating device to be utilized in combination with the aforesaid smoke detector is implemented by the provision of a suitably located auxiliary light source such that light therefrom can be selectively directed on the reflected photocell, thereby to trigger the alarm or actuating device. Thus, instead of interfering with the light from the main light source by interposing a wire or the like such as to scatter the light to the reflected cell, a rotatable cylinder having an appropriate slot is interposed in the light path between the aforesaid auxiliary source and the reflected cell.
Accordingly, advantage is taken of the fact that the auxiliary light source is already adapted to serve as a "power on" indicator in the smoke detector; moreover, the rotatable cylinder affords a more rugged and effective means of simulating the desired effect directly without the need for uncertain scattering which might possibly arise because of incorrect variable placement of the main light source or of the wire typically used for scattering purposes.
The object of promoting efficient air flow is fulfilled by the provision of a sensor head which houses or contains the main light source and the reflected photocell. As a result, it will be appreciated that undesirable variations in locations of elements is obviated; that is to say, the disposition of both the light source and the reflected cell within a common head or block of material eliminates the possibility of variation, during assembly, of their positioning on a circuit board or the like.
Other and further objects, advantages and features of the present invention will be understood by reference to the following specification in conjunction with the annexed drawings, wherein like parts have been given like numbers.